pym was in his lab cooking up some magical sciency potions when his work turned into a portal and transported him to the gundamn universe. This is during the original one year war gundam universe so the Zakus are there taking over the city in the name of of the Principality of Zeon.Pym doesnt know whats going but he sees 3 giant robots destroying the city so he juices up and turns into giant man( thanks to his sweet science magic). The zeon ms pilots think hank is a federation gov expirement gone horribly right(giant soldiers could tip things to the federation) so they decide to hault their current mission to bring this new find to zeon scientist.
Fight takes place in the middle of downtown the Zakus are armed with their axes only making this a hand to hand fight. i think giving the zakus guns would be the equivalent of hank vs 3 dozen bullets so no guns, bazookas only axes. Zakus cannot fly around as seen in MS gundam 0083 stardust memory but walk on the ground like in the 08th MS team but they can use their jet packs for a boost.